The present invention relates generally to a system and method for the compression of digital signals. More specifically, the present invention relates to reducing the file size or the bit rate required by a system using binary arithmetic encoding to entropy encode a digital signal such as a digital image or digital video.
Throughout this specification we will be using the term MPEG as a generic reference to a family of international standards set by the Motion Picture Expert Group. MPEG reports to sub-committee 29 (SC29) of the Joint Technical Committee (JTC1) of the International Organization for Standardization (ISO) and the International Electro-technical Commission (IEC).
Throughout this specification the term H26x will be used as a generic reference to a closely related group of international recommendations by the Video Coding Experts Group (VCEG). VCEG addresses Question 6 (Q.6) of Study Group 16 (SG16) of the International Telecommunications Union Telecommunication Standardization Sector (ITU-T). These standards/recommendations specify exactly how to represent visual and audio information in a compressed digital format. They are used in a wide variety of applications, including DVD (Digital Video Discs), DVB (Digital Video Broadcasting), Digital cinema, and videoconferencing.
Throughout this specification the term MPEG/H.26x will refer to the superset of MPEG and H.26x standards and recommendations.
A feature of MPEG/H.26x is that these standards are often capable of representing a video signal with data roughly {fraction (1/50)}th the size of the original uncompressed video, while still maintaining good visual quality. Although this compression ratio varies greatly depending on the nature of the detail and motion of the source video, it serves to illustrate that compressing digital images is an area of interest to those who provide digital transmission. MPEG/H.26x achieves high compression of video through the successive application of four basic mechanisms:
1) Storing the luminance (black and white) detail of the video signal with more horizontal and vertical resolution than the two chrominance (colour) components of the video.
2) Storing only the changes from one video frame to another, instead of the entire frame. Thus, often storing motion vector symbols indicating spatial correspondence between frames.
3) Storing these changes with reduced fidelity, as quantized transform coefficient symbols, to trade-off a reduced number of bits per symbol with increased video distortion.
4) Storing all the symbols representing the compressed video with entropy encoding, which exploits the statistics of the symbols, to reduce the number of bits per symbol without introducing any additional video signal distortion.
With regard to point 4), the symbols may be encoded as codewords in a variety of ways. One such encoding is binarization. Small codewords are well handled by unary or exp-Golomb binarizations while large codewords are best represented with the binarization limited to a reasonable length. Thus there is a need for a method and system binarization system that retains the most valuable properties of the unary and exp-Golomb binarizations. That is, small codewords should be distinguishable as with a unary binarization, while large codewords should have their binarization limited to a reasonable length. A binarization that simultaneously satisfies these two requirements will reduce the complexity and the bitrate/size for compressing and decompressing video, images, and signals that are compressed using binary arithmetic encoding for entropy encoding. The present invention addresses this need.
The present invention is directed to a method of binarization, the method comprising the step of determining if a code symbol index value is less than a threshold value, if so then constructing a codeword using a first binarization model; else constructing a codeword using a second binarization model.
The present invention is also directed to a binarization system, the system comprising means for determining if a code symbol index value is less than a threshold value, if so then utilizing means for constructing a codeword using a first binarization model; else utilizing means for constructing a codeword using a second binarization model.
The present invention is further directed to a computer readable medium containing instructions for binarization, comprising instructions for determining if a code symbol index value is less than a threshold value, if so then constructing a codeword using a first binarization model; else constructing a codeword using a second binarization model.